This invention pertains to remote expansion of tube end joints such as prior to welding. It pertains particularly to an elongated tube expander tool and method for remotely expanding tube ends to provide a close fit in mating tubes prior to making a remote weld joint inside the tubes.
In steam generators for nuclear power plants, bundles of U-shaped heat exchanger tubes are usually provided which are welded into a relatively thick tube sheet. During operation of such steam generators over an extended period of time, such as 10 years or more, a corrosive sludge material forms and accumulates on the inner upper surface of the tube sheet. This accumulated sludge material causes corrosion of the heat exchanger tubes to an extent of potential or actual tube failure. To correct this serious problem without undesirable disassembly or replacement of the heat exchanger, it is necessary to remove the old deteriorated tube end portions from the tube sheet and replace them with new tube portions which are positioned and welded pressure-tightly into place, without need to remove and dismantle the entire heat exchanger assembly. However, because of the remote and relatively inaccessible location of the tubes and the radioactive environment which is usually involved, such tube replacement is very difficult to accomplish reliably and safely. Thus, providing a suitable solution to this tube replacement problem by using remotely operated tube removal and replacement apparatus and preparation of the replacement tube joint in the existing tube ends for reliable seam welding has been needed, particularly for heat exchangers used in the nuclear power industry, and has led to the present invention.